1. Field of the Invention
In general the field of endeavor to which this invention pertains is the radio communication systems and components and related methods. Specifically, it concerns antenna arrays for wireless radio communication or surveillance.
2. Description of the Prior Art and Related Background Information
Many present day and future RF and microwave systems need antennas, which are compact, high gain and cover extremely wide bands to minimize the size impact and number of antennas needed. On mobile platforms, this lowers cost, drag, and observability; on fixed platforms, such as rooftops and towers, this lowers cost, which is directly a function of real estate utilized.
Omnidirectional antennas are often required for mobile systems where the azimuth angular direction between the base station and the mobile platform is unknown, or in point-to-multipoint system base stations where uniform coverage in all directions is critical. In these systems, it is often the minimum antenna gain in azimuth that is the figure of merit, so there is a large incentive to make the gain as uniform in azimuth as possible. In addition, these systems often need the highest gain fixed on the horizon.
Sectoral antennas are often required for point-to-point systems and the highest gain possible in a fixed direction is desirable.
Prior to this invention, omnidirectional antenna solutions typically had to choose between designs that optimized gain, but only could cover a narrow band of frequencies, or optimized bandwidth, but sacrificed gain. Some have moderate gain over a large bandwidth but they are so large as to be undesirable in mobile applications. Many solutions do not have true omnidirectional uniform gain in azimuth.
A dipole antenna has omnidirectional coverage, but only 2 to 3 dB gain on the horizon. To increase the gain an array of dipole antennas stacked in elevation is needed. These are usually called collinear arrays. The issue is how to feed the stacked dipoles. If the dipoles are fed in series, then as the frequency changes, the beam scans in elevation, which can severely limit the bandwidth if there is a high gain spec on the horizon. If they are fed from the side with some from of planar corporate feed, also known as a true time delay network, then the feed interferes with the pattern in the azimuth plane and tends to make the antenna too large.
Many previous solutions have used biconical dipoles to improve bandwidth, but need to go to multi-element or stacked arrays of such dipoles to improve the gain. In this case, per the description above, due to issues with the feed network, only moderate gains or bandwidths are achieved.
Sectoral antennas are typically patch arrays, which are very compact but very narrow band or dish antennas, which are moderately compact and medium bandwidth, or horn antennas, which can be extremely broadband, but also are extremely bulky.